The present invention relates to nuclear fuel assemblies, and more particularly, to applying wear and/or corrosion-resistant coatings on fuel assembly components.
It is well known among nuclear fuel engineers, that corrosion and wear can occur in a variety of locations on a nuclear fuel assembly. These locations include the inside surface of nuclear fuel rods (i.e., the fuel cladding ID surface), and the inside surface of control rod guide tubes.
Attempts to reduce corrosion and wear within fuel rod tube cladding, are represented by U.S. Pat. No. 4,541,984 (Palmer), which discloses a getter-lubricant coating, preferably with a burnable poison material. The lubricant reduces stresses on the cladding resulting from the expansion or misalignment of fuel pellets acting against the inside clad surface. Furthermore, the getter material absorbs hydrogen atoms which would otherwise contribute to the initiation and propagation of corrosion, particularly at the areas of high stress within the cladding.
U.S. Pat. Nos. 4,376,092; 4,135,972; 4,284,475; 4,333,798 all disclose a sleeve of one form or another secured within a control rod guide tube, to protect the guide tube from excessive fretting wear. This wear results from vibratory movement of the control rod leading end, which remains in the upper portion of the guide tube even when the control rod is fully withdrawn from the reactor core. Typically, these wear sleeves are coaxially placed within the guide tubes in the upper end (top) of the fuel assembly. To accommodate these sleeves the guide tube is bulged to a larger diameter and the top grid likewise requires additional operations to open its guide tube cells to a larger size.
A number of techniques have been disclosed in the prior art, for coating the outside of fuel assembly components, for corrosion and/or wear resistance. U.S. Pat. Nos. 4,724,016 (Anthony) and 5,026,517 (Menken et al), are representative of these techniques. Such techniques are not readily adaptable for coating the inside surfaces of fuel assembly tubular components, which are generally at least 10 feet long, and have IDs which are often less than 0.5 inch.